The invention relates to a voltage monitoring device for monitoring two different supply voltages received by an electronic component.
The supply voltages required, for example, for a microcontroller are normally produced from an operating voltage by integrated voltage regulators.
Published, Non-Prosecuted German Patent Application DE 36 12 237 A1 discloses a configuration for monitoring voltages which are supplied via a multiplexer to an analog/digital converter and are compared in a microprocessor with stored limit values. The comparison result is displayed in a display apparatus.
A voltage monitoring IC which initiates a reset signal when the voltage to be monitored falls below a specific voltage level is known from the reference DE-Z xe2x80x9cDESIGNandELEKTRONIKxe2x80x9d [Design and Electronics], Issue 5 dated Mar. 1, 1998, pages 13 and 16.
As a rule, integrated voltage regulators are equipped with an integrated voltage monitorxe2x80x94formed of an analog/digital converter and a comparatorxe2x80x94and emit a reset signal if their output voltage, a supply voltage for the electronic component, is outside a defined voltage range.
Integration of the voltage monitors on the respective voltage regulator results in that linear independence between the output voltage and the voltage monitoring of each voltage regulator and the output voltages of the two voltage regulators is no longer ensured, since output voltage production and voltage monitoring of a voltage regulator use the same reference voltage, or the two regulators can produce different reference voltages. Errors resulting from unacceptably high drift of the reference voltage of one voltage regulator cannot be identified owing to joint use for voltage production and monitoring.
It is accordingly an object of the invention to provide a voltage monitoring device for monitoring two different supply voltages received by an electronic component which overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which a linear independence between the output voltage and the voltage monitoring of a voltage regulator and the output voltages of the two voltage regulators is ensured.
With the foregoing and other objects in view there is provided, in accordance with the invention, a combination of an electronic component and a voltage monitoring device for monitoring two supply voltages including a larger supply voltage and a smaller supply voltage to be supplied to the electronic component. Each of the supply voltages is produced from an operating voltage supplied to a respective integrated voltage regulator and the respective integrated voltage regulator has a regulator voltage monitor for monitoring an output voltage of the respective integrated voltage regulator and the output voltage being one of the supply voltages supplied to the electronic component. The voltage monitoring device includes a ratiometrically operating analog/digital converter having a reference input receiving the larger supply voltage, a measurement input receiving the smaller supply voltage, and an output. The ratiometrically operating analog/digital converter generates a digital value provided at the output. A window comparator is connected to the ratiometrically operating analog/digital converter and receives the digital value. The window comparator compares the digital value with predetermined limit values including an upper limit value and a lower limit value, the window comparator generates a reset signal if the digital value is greater than the upper limit value or is less than the lower limit value.
In accordance with an added feature of the invention, the electronic component is a microcontroller and the ratiometrically operating analog/digital converter is integrated the microcontroller, and the window comparator is performed by software in the microcontroller.
With the foregoing and other objects in view there is provided, in accordance with the invention, a circuit formed of integrated voltage regulators receiving a supply voltage and outputting two supply voltages including a larger supply voltage and a smaller supply voltage. Each of the integrated voltage regulators has a voltage monitor for monitoring the supply voltages. The voltage monitor has an analog/digital converter and a window comparator connected to the analog/digital converter. The integrated voltage regulators output a reset signal if one of the supply voltages being monitored is outside of a defined voltage range. An electronic component includes a ratiometrically operating analog/digital converter having a reference input receiving the larger supply voltage, a measurement input receiving the smaller supply voltage, and an output. The ratiometrically operating analog/digital converter generates a digital value which is provided at the output. A further window comparator is connected to the ratiometrically operating analog/digital converter and receives the digital value. The further window comparator compares the digital value with predetermined limit values including an upper limit value and a lower limit value, further window comparator generates a further reset signal if the digital value is greater than the upper limit value or is less than the lower limit value.
In accordance with a concomitant feature of the invention, the electronic component is a microcontroller.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a voltage monitoring device for monitoring two different supply voltages received an electronic component, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.